Among the various thermoset polymers, epoxy resins provide superior overall performance, such as good mechanical properties, chemical resistance, and low shrinkage. Therefore, epoxy resins are high-performance systems for use in coating, adhesive, civil engineering, structural, electronic and composite applications.
In 1907, phenolic resins were the first thermoset resins to be synthesized commercially. These resins have excellent fire performance, good dimensional stability, excellent thermal insulation properties, and are cost effective. These properties enable phenolics to be used in household appliances, business equipment, wiring devices, automotive electrical systems, and mass transit.
Fiber reinforced plastics (FRPs) are the most widely used composites. In general, fibers are the principal load-carrying members, while the surrounding plastic matrix keeps the fibers in the desired location and orientation, acting as a load transfer medium. The plastic also protects the fibers from environmental damage due to exposure to elevated temperature and humidity. Fiber-reinforced composites have low specific gravity, high internal damping, and high strength-to-weight ratio and modulus-to-weight ratio. There have been numerous applications for FRPs, and additional applications are continually sought, due to the attractive properties. In the FRP art, the terms “long fiber” and “short fiber” are commonly used to designate fibers and will be understood by those of skill in the art.
A “nanocomposite” is a composite containing a disperse material with at least one dimension that is smaller than about 100 nm in size. Due to the nanoscale dispersion and the high aspect ratios of the inorganic clays, polymer-layered silicate nanocomposites (PLSNs) exhibit light weight, dimensional stability, heat resistance, and a certain degree of stiffness, barrier properties, improved toughness and strength with far less reinforcement loading than conventional composite counterparts. The synthesis and characterization of PLSNs has become one of the frontiers in materials science.
Since the discovery of carbon nanotubes (CNTs), many people have studied the properties of polymer-carbon nanotube composites. However, the high cost and low volume of production of the CNT have greatly limited product development and application. Carbon nanofibers (CNF), defined as carbon fibers with diameters of up to 200 nm (and typically in the 100-200 nm range) and lengths of up to about 100 microns, may serve as a substitute for the carbon nanotubes. Recent studies indicate that polymer-carbon nanofiber composites (PCNFCs) have properties similar to polymer-carbon nanotube composites. These CNF nanocomposites can be used to make conductive paints, coatings, films, tubes, sheets, and parts for electrostatic painting, electro-magnetic interference and electro-static discharge applications. In addition, these composites also provide improved strength, stiffness, dimensional stability and thermal conductivity. It makes the PCNFCs a very promising material for a wide range of applications in automotive, aerospace, electronic and chemical industries.
Although fiber-reinforced plastics (FRP) have good mechanical properties, an interface exists between the polymer matrix and the individual fibers. This interface, which represents a substantial area, is subject to diffusive attack by water and other small molecules. This can cause a substantial drop in interfacial strength and failure of adhesion between the components. Under tension, compression, shear, or impact, failure of the polymer matrix may also take place.
A problem continually encountered in preparing nanocomposites has been the difficulty in properly dispersing the nanoparticles in the continuous polymer phase. For example, it is often difficult to load more than about 10 weight % of nanoparticles into the continuous phase. By way of comparison, a highly-loaded FRP can often contain greater than 50 weight % of the disperse fiber phase. Not unexpectedly, the enhancement of mechanical properties of the continuous phase polymer in a typical PLSN or PCNFC is relatively low compared with the enhancement of mechanical properties in a typical FRP. When this is combined with the high cost of the nano-scale material, it would be surprising if nanocomposites would have already made significant market penetration.
It is therefore an object of the present invention to provide a composite material that effectively combines advantages of a disperse fiber phase and a disperse nanoparticle phase.